1. Field of the Invention
The present invention relates to a reception device for a radio communication system for receiving subscriber signals via a radio interface wherein the reception device contains a device for determining a number of active subscribers from a total number of subscribers that are assigned to the radio interface and further contains a detection device for detecting at least one subscriber signal.
2. Description of the Prior Art
Radio communication systems serve for the transmission of subscriber signals via a radio interface with the assistance of high-frequency oscillations. Such radio communications systems are, for example, mobile radio telephone networks or devices for wireless subscriber connection to a fixed network. When the subscriber signals of various subscribers are transmitted via the radio interface, it is called a multi-subscriber message transmission system. Time-division multiplex, frequency-division multiplex or code-division multiplex methods can be employed for separating the subscribers. It is also possible to combine these methods.
When, according to a multi-subscriber message transmission system, for example, K different subscribers are allocated to the radio interface formed by a channel, the corresponding reception device must be able to undertake a separation of the subscriber signals. Depending on the number of different subscribers, this leads to a considerable detection outlay in the reception device, since the actual conditions on the radio interface are unknown to the reception device.
U. Mitra, H. V. Poor, xe2x80x9cNeural Network Techniques for Multi-User Demodulationxe2x80x9d, Proceedings of the international conference on neural networks, San Francisco, Mar. 28-Apr. 1, 1994, Vol. 3, pp. 1538-1543, and B. Aazhang, B.-P. Paris, xe2x80x9cNeural Networks for Multi-User Detection in Code-Division Multiple-Access Communicationsxe2x80x9d, IEEE Transactions on Communications, Vol. 40, No. 7, Jul. 1, 1992, pp. 1212-1222, disclose detection principles for CDMA transmission methods suitable for a different number of subscribers. EP-A-0 526439 discloses a CDMA receiver wherein only the strongest signals are evaluated. Further, P. Jung, B. Steiner, xe2x80x9cKonzept eines CDMA-Mobilfunksystems mit gemeinsamer Detektion fxc3xcr die dritte Mobilfunkgenerationxe2x80x9d, Nachrichtentechnik/Elektronik 45 (1995), March/April 1995, pp. 24-27, discloses a CDMA transmission method in time slots.
The invention present is, present therefore present direct toward reducing the detection outlay.
The inventive reception device for a radio communication system for the reception of subscriber signals via a radio interface contains a device for determining the plurality Kxe2x80x2 of active subscribers from a set of K subscribers allocated to the radio interface and contains a detection device for detecting at least one subscriber signal. A signal mix present at the reception device can be processed better and the subscriber signals can be detected better since, given a plurality Kxe2x80x2 less than K of active subscribers, the set of subscribers to be taken into consideration in the detection is reduced.
According to an embodiment of the present invention, the reception is improved further when the device for determining the Kxe2x80x2 active subscribers is connected such to the detection device that the plurality Kxe2x80x2 of active subscribers and their identity is communicated to the detection device. When the Kxe2x80x2 active subscribers are known to the detection device on the basis of their identify, then a plurality K-Kxe2x80x2 of subscribers can remain out of consideration in the separation of the subscriber signals.
When the subscriber signals arrive at the reception device by radial blocks, then the device for determining the Kxe2x80x2 active subscribers advantageously determines these from the subscriber signals related to radial blocks. Since the plurality of the Kxe2x80x2 active subscribers can change from radial block to radial block, a determination of the Kxe2x80x2 active subscribers from the subscriber signals constantly gives the reception device current values that are required for the detection. Some other signaling regarding the plurality of Kxe2x80x2 active subscribers thereby need not be undertaken. A plurality of radial blocks can be combined for a higher measuring position in this evaluation related to radial blocks.
The inventive reception device is particularly advantageous when the subscriber signals are primarily separated by a fine structure. Such a fine structure is established, for example, in the code-division multiplex method (CDMA-code division multiple access) since a subscriber-related code is allocated to every subscriber at the transmission side. As the corresponding reception device knows at least the code of the at least one subscriber signal.
The separation of the subscribers thus occurs via their subscriber code. The subscriber signals are modulated with this subscriber code. When the subscriber signals, as disclosed, for example, by German Letters Patents DE 41 21 356 C2 or DE 43 29 320 A1, are detected according to what is referred to as the JD (joint detection) CDMA method, then it is particularly significant that the plurality of subscriber codes to be taken into consideration is reduced. The inventive reception device offers particular advantages here.
According to a further embodiment of the reception device, the device for determining the Kxe2x80x2 active subscribers is connected such to the detection device that the fine structures of the Kxe2x80x2 active subscribers are communicated to the detection device. The fine structures that are thus communicated serve the JD-CDMA detection algorithm for separating one or more subscriber signals accordingly the influence of the respectively other Kxe2x80x2xe2x88x921 active subscribers is also taken into consideration. The device for determining the Kxe2x80x2 active subscribers is advantageously configured such that a respective test quantity is determined from the K possible subscriber signals and is compared to a threshold. Which of the K subscribers is, in fact, active at the moment derives from this comparison.
According to an a further embodiment, this test quantity has been determined from a quantity proportional to the energy of a channel pulse response of the respective subscriber signal. A channel model of the reception device is required for distortion-correction of subscriber signals, for which reason a channel pulse response is determined for each subscriber signal and the channel model can be balanced accordingly. The energy of the channel pulse response or, respectively, equivalent quantities such as the power, is a suitable quantity for determining the activity of a subscriber. Alternatively, the test quantity quantity can be determined from a sum of the amounts of samples of the respective subscriber signals; for example, of the data-bearing part of the subscriber signal. Given a digital transmission, samples from which the subscriber signals are subsequently to be reconstructed are identified at the reception device. A conclusion about the activity of the respective subscriber is all the more reliable the more strongly the samples contrast with noise on the radio interface.
According to further embodiments of the present invention, the test quantity can be determined from a data-carrying part of the respective subscriber signal (particularly suitable when no balance values are available), i.e. from the samples for corresponding data symbols, or from a test sequence of the respective subscriber signal. A test sequence is thereby a plurality of symbols that is sent by the respective transmission device in addition to the transmitted data and that is known undistorted at the reception device. For example, the reception device can determine the channel pulse response from a comparison of known test sequence to received test sequence.
When the set of possible fine structures is limited, then the advantage arises for the reception device that the set of K subscribers can also be limited and the outlay for determining the Kxe2x80x2 active subscribers is reduced.
It must be noted for defining the threshold that this not be placed too low since this leads to an incorrect determination of active subscribers. However, the threshold also should not be set too high since subscribers who are, in fact, not active but transmit with a low transmission power are not detected. Advantageously, accordingly, the threshold is defined proportional to the signal/noise ratio of the respective subscriber signal or proportional to the average signal/noise ratio of a plurality of subscriber signals.
It is also possible to orient the threshold based on the signal/noise ratio of the strongest subscriber signal. When a communication connection covers a plurality of channels, it is advantageous that the threshold is respectively proportional to the weakest of the subscriber signals so that none of the channels is lost. Advantageously, the thresholds for the individual subscribers of the K subscribers can be individually set in order to achieve a best possible adaptation to the subscriber-related conditions of the radio interface.
The inventive reception device is particularly suited for utilization in base stations or mobile stations of a mobile radio telephone system or as a radio station of a wireless access network (RITL radio in the loop).